Bonds are used, for example, for constructing vertical hybrid integrated components. Components of this type generally include multiple MEMS and/or ASIC elements whose element functions complement each other. Vertical hybrid integrated sensor components which include a MEMS element and an ASIC element are important in particular. The micromechanical structure of the MEMS element is used to detect a measured variable which is converted into an electrical measuring signal with the aid of circuit elements of the MEMS element. These measuring signals are then processed and, if necessary, evaluated using the circuit functions of the ASIC element.
The elements of a vertical hybrid integrated component are situated above one another in the form of a chip stack and are bonded to one another in such a way that further repackaging for the second level assembly on an application circuit board is not necessary. For this purpose, the mechanical connection between the individual elements must, on the one hand, be permanently stable and, on the other hand, also circumferentially tightly closed in order to protect the element functions against harmful environmental influences, e.g., dust particles, moisture, and gases.
During the manufacture of vertical hybrid integrated components, the individual element components are not only generally produced in the wafer composite. Their assembly also takes place in the wafer composite during a wafer bonding process. The components are frequently even separated only after testing and calibration at the end of the manufacturing process.
In practice, wafer bonding processes are mostly employed during which one or also both element surface(s) or wafer surface(s) to be bonded are provided with a structured bonding layer. These bonding processes include glass frit bonding, during which low melting lead glass is used as the bonding layer, and metallic bonding processes, such as the thermocompression bonding processes Au—Au bonding, Cu—Cu bonding and Al—Al bonding, eutectic bonding processes Au—Si bonding, Al—Ge bonding, Al—Au bonding, and Al—Si bonding as well as solid-liquid interdiffusion (SLID) bonding involving Cu/Sn and Au/Sn.
Since the glass frit technique requires a relatively large chip area in order to ensure a hermetically sealed and permanently stable bond, metallic bonding processes are increasingly used. Although the space requirement for a hermetically sealed and mechanically solid connection is considerably smaller with this technique, it imposes significantly higher requirements on the wafer surfaces to be bonded, in particular on their planarity and purity. Since the wafer bond is established in this case with the aid of interdiffusion or by fusion of the bonding areas, the latter must be brought into intimate contact. For this purpose, very high contact pressures in the magnitude of up to 100 kN are applied during the entire bonding process and onto the entire bonding area.